So far I haven't come across them in 1871, still looking, but it doesn't seem as though you have had a full transcript of the 1861 as there are other children after Harriett.
RG9/809 Folio 103 Page 23
Rye Street, Bishops Stortford
John Parker Head M 39 Brewers Lab
Emma Wife M 39
George Son 14 " "
Lydia daur 13 Scholar
Elizabeth " 13 "
Charles Son 10 "
Drusilla daur 8 "
Emily " 6 "
Harriett " 5 "
Alice " 2 "
John Son 8 mos
All born Herts Bps Stortford
I did think that a name like Drusilla wouldn't be so difficult to find later, but its not proving that way, do you have any other details of marriages/deaths apart from the parents which would give indications as to who would be in the family?